Chapter 1 - Núria BONADA

Local scale: Optimums and tolerances in Trichoptera
Hydropsychids (e.g., H. exocellata, H. brevis, H. infernalis, H. gr. pellucidula). Most of the
caddisflies have the optimums at sulphates concentrations under 250 mg/l, indicating their
preferences for basins without gypsum geology, as Micrasema sp., Sericostoma sp. or Halesus
sp. The glossosomatid Agapetus sp. is very frequent in chloride concentrations over than 200
mg/l and conductivities of 1802 µS/cm. However, Hydroptila sp. although having the optimum
of sulphates and chloride under 250 mg/l and 99 mg/l respectively, presents the widest
tolerance to conductivity, beeing able to survive at more than 4000 µS/cm.
Ecological profiles for caddisfly taxa
Ecological profiles for each genus/species and family levels have been figured out using
tolerances for six measured environmental variables (oxygen, suspended solids, P-phosphates,
ammonium, sulphates and chloride) (Figures 6, 7, 8, 9 and 10). N-nitrites have been omitted
because the high tolerance values in some species with low optimums, what could be an error
in chemical analysis. Profiles have been drawn as a polyhedral figure (Figure 6). Each axis
represents the tolerance range constrained between 1 and 0. The extremes of each axis indicate
the intolerance of taxa to high values of chemical parameters (i.e., suspended solids, P-
phosphates, ammonium, sulphates and chloride) or to low values of oxygen. When combining
the tolerance ranges for all axes a shaded figure appears indicating the degree of tolerance for
each taxon, whereas the non-shaded area displays the degree of intolerance to pollution.
Thereby, caddisfly very sensitive to all environmental variables will have narrow shade and large
empty areas, in contrast to very tolerant taxa. The degree of intolerance score (DIS) has been
measured using the following formula:
5
∑
i=
1
DIS= (1-maxi)
+ minj
for i=chemical variables and j=oxygen concentration
This score varies between 0 to 6 and give us an idea of the sensitivity of each species to
pollution (higher the value, more intolerant).
313